Conventionally, as one of the power modules, there have been known power modules in which a power device(s) (power chip(s)) including semiconductor device (s) as an Insulated Gate Bipolar Transistor (IGBT) is mounted on a leadframe, and the whole system is molded with a resin. Since such a semiconductor device produces heat during an operating state, it is common to dispose a heat sink for dissipating heat on a back side surface of the leadframe in order to cool the semiconductor device.
Moreover, in order to improve cooling performance, there have been known: inverter apparatuses for water-cooling of whole of a heat sink (or also referred to as “liquid cooling”) with a coolant passage formed on a back side surface of the heat sink; and semiconductor devices configured so that a rectangular parallelepiped having four side surfaces on which switching devices having large frequencies are respectively arranged in a hollow form in order to suppress a temperature increase of the devices.